The present invention relates to a new and improved method of placing into operation one of a number of power converter units or groups which as concerns the direct-current are connected in series and as concerns the alternating-current in parallel, of a power converter operating in the rectifying mode and inverting mode, respectively, of a high-voltage direct-current transmission installation, wherein a bypass or shunt switch is connected in parallel with each power converter group.
Such techniques are known in this technology from, for instance, German Patent No. 2,514,227, published Sept. 9, 1976, and German Patent Publication No. 2,512,364.
For power converter groups or units connected in series during systems operation there arises the task of incorporating during the operation of a power converter group a further power converter group into the current or power circuit without first having to interrupt the operation. To this end, the power transmission either should not be effective at all or in a predetermined manner, for instance approximately with a linear ascent within a desired settable time. It is desired that the thus arising reactive power fluctuations at the terminal stations should be maintained as brief in duration as possible or that, in the event there is accomplished an increase in the active or true power, the reactive power should increase approximately proportionally with the active power.
The new group of power converters which is to be placed into operation is initially shunted by a bypass or shunt switch which must be opened during placement into operation of the power converter group. The switch current also must be commutated to the power converter group without endangering the switch.
With the heretofore known methods this is accomplished with the aid of a special start-up regulation. However, this is associated with the drawback that prior to opening of the bypass or shunt switch there is regulated into the power converter the entire current flowing in the direct-current line. During the regulation or adjustment time the power converter group which is to be placed into operation is in its zero voltage operational mode. Its apparent power therefore is practically pure reactive power and at the rated current it is approximately as great as its rated power.
During the regulation or adjustment time of the start-up regulator, which amounts to about 0.5 to 1 second, the generators of the power network have the opportunity of setting the additionally required reactive power. As soon as the bypass switch has been opened and the power converter group which has been placed into operation runs-up with its voltage there is reduced the power converter-reactive power. In the case of two power converter groups or units which are connected in series the line pole at the end of the compensation operation, with constant transmission power, carries one-half of the current at twice the potential. The reactive power of both power converter groups is approximately exactly as great as the original power converter-reactive power (at full current and half line voltage). Therefore, the generators must again be returned to their old reactive power value. This is also true for the placement into operation of more than two power converter groups connected in series. To avoid an excess of reactive power and thus overvoltages during the start or running-up of the power converter which is to be placed into operation, the run-up control of the direct-current voltage, with the heretofore known methods, disadvantageously must be accomplished so slowly that the reactive power regulation of the network can follow.